Considering the range of temperatures aircraft can fly in, you might think extreme heat would not put much stress on a modern plane. But extreme heat can have a big impact on a plane’s ability to operate efficiently and safely. As a result, extreme heat is a risk many airlines have to manage and mitigate.

Extreme heat can have a big impact on an aircraft’s safe operation. Photo: Ontario International Airport

Extreme heat can push an aircraft’s safe environmental envelope

Modern aircraft have what’s called an environmental envelope (which includes a maximum static air temperature) in which they can safely fly. There is a well-reported 2017 incident in Phoenix, Arizona, when several Bombardier CRJ flights were canceled because the outside air temperature was averaging 49°C – beyond that aircraft’s maximum allowable ambient operating temperature.

Extreme heat is becoming more common. With their acres of asphalt and concrete absorbing and reflecting sunlight, airports can become temperature hotspots. Add in some wind, and it can prove a volatile mix.

Extreme heat can have a significant impact on an aircraft’s flying ability. High ground temperatures reduce air density, especially in dry climate countries. Aircraft need lift to take off, and lift is affected by the density of the surrounding air.

When the air density is low, planes need to travel faster down the runway to produce enough lift to take off. That’s now necessarily a problem if you are in a lightly loaded A220 powering down a three-kilometer-plus runway. But if you are in a heavily loaded Boeing 777, there’s the risk of not enough runway.

In extreme heat conditions, heavily loaded big planes need extra runway length to take off. Photo: Ontario International Airport

Damp extreme heat can be as problematic as dry extreme heat

It is the pilot’s job to calculate that risk and, if it exists, to mitigate the risk. That can be achieved by reducing the plane’s weight – best done by removing passengers and/or cargo. Aside from the inconvenience, this has an economic cost for the airline.

In equatorial parts of the world, where it’s typically hot and damp, the air density may be higher, but extreme heat can produce other types of risks. Convective cumulonimbus clouds and storms are byproducts of extreme heat in humid climates, and both are risks for any aircraft.

Extreme heat also impacts aircraft engines. An engine’s extreme heat tolerance will vary by type and stage of flight, but normally there is a time limit attached. Sitting on the apron at a hot airport, there’s the possibility an engine will reach its maximum operating limits before it produces the thrust needed to takeoff. Extreme heat can also adversely impact a plane’s aerofoil performance.

Then you have myriad other potential problems. Extreme heat can potentially lead to overheating brake components, bleed air systems, and electronic equipment. Cabin air conditioning can fail.

Extreme heat in wet climates brings its own set of risks. Photo: Ontario International Airport

Extreme heat risk can be mitigated

What’s the solution? Stop flying to hot climate airports? Build longer runways? None of these are viable options. Experts suggest mitigation. Leaving flaps and slats partially extended on some aircraft types can increase airflow and help combat temperature rises. Venting the plane on the ground can help reduce temperatures.

Then there are logistical solutions – flying heavier planes during cooler times in the day and lightly loading planes when extreme heat is expected. Other experts suggest adjusting flights times. Of course, these are all easier said than done. Operating an airline is a complex business and learning to manage extreme heat scenarios is just one part of that.

from Simple Flying

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